vice president joe biden today. >> how they can justify raising taxes on the middle class has been buried the last four years. how in lord's name can they justify raising their taxes? >> reporter: the romney campaign quickly seized on that comment. arguing the president's policies have hurt the middle class. taking a breather from his preparations outside las vegas today. he visited the hoover dam. >> it's spectacular and i've never seen it before. >> reporter: aides say he's been calling his family to unwind each night. while the two campaigns have gone out of their way to lower expectations, surrogates on both sides today acknowledge the debate will be a pivotal moment. >> i think it's important for viewers to get a chance to do comparison shopping. seeing the two candidates face to face, head to head. >> this cannot be about decibels. what it does have to be about, particularly for governor romney, is details. >> reporter: romney who has 23 primary debates under his belt, says he doesn't like formal debate prep, says it feels too artificial. instead, opting for more casual sessions. ad